1. Field of the Invention
The present invention relates to fiber optic, cross-connect switches employing individual tiltable mirrors which direct signal beams within the switches between the desired optical fibers in telecommunications systems, and more specifically to an alignment system for such switches.
2. Discussion of the Related Art
Optical telecommunications systems are increasingly replacing cable and other wire-based electronic telecommunications systems. This is directly related to the speed of light at which data is transmitted through optical fibers, the ability to transmit data in parallel using different wavelengths of light, the ability to simultaneously transmit data in both directions along each optical fiber, and the increased miniaturization and lower cost of the optical components necessary to build optical telecommunications systems.
Optical telecommunications systems typically require switching of the data transmitted by the light from the end of one optical fiber to another which requires mechanical switching of the light path. Advances in miniaturization of optical switching based on micro-electromechanical system (MEMS) mirrors are now making optical communications systems both more economical to build and more reliable in use. Such MEMS mirrors are typically constructed as a two dimensional array of tiltable mirrors as part of an optical cross-connect switch, which mirrors direct light from an emitter end of one optical fiber to a target end of another optical fiber. Each end of an optical fiber can simultaneously be both an emitter end and a target end. The tiltable mirrors can simultaneously rotate about individual “X” and “Y” axes, each tiltable mirror being individually suspended above a base or substrate by a plurality of flexible suspension arms attached to the substrate. The signal beam travels using free-space light transmission between the optical fibers, making numerous configurations and sizes of optical cross-connect switches and systems possible. The tiltable mirrors are tilted by electrostatic, electro-magnetic, piezoelectric, or thermal actuation forces which are induced between the tiltable mirrors and the substrate through a controller. The MEMS mirror arrays may have on the order of 1000×1000 individual mirrors sized with a typical diameter or diagonal in the range of about 300 um to about 1000 um. The tiltable mirrors can be shaped as a circle, ellipse, polygon, or rectangle, and can be planar or curved, with planar being typical due to ease of construction. The signal beam is typically a circular beam. Respective circular collimating lenslets are typically, but optionally, disposed closely adjacent the ends of the optical fibers to focus the signal beams as they exit the emitter ends and enter the target ends thereof.
Other components used in optical telecommunications systems may include beam combiners and beam splitters for multiplexing and demultiplexing optical signal beams having different wavelengths. Such beam combiners and beam splitters typically utilize a dichroic mirror disposed at an angle to the path of the signal beams. The dichroic mirrors function in a known manner, reflecting part or all of a preselected wavelength of light while transmitting the remaining wavelengths, or by transmitting the preselected wavelength of light and reflecting the remaining wavelengths. Therefore, either the preselected wavelength or the other wavelengths of light are passed through the dichroic mirror in a substantially straight path while part or all of the other wavelengths are reflected at a predetermined angle relative to the angle of incidence of the light beam.
Another component used in various arts are charge-coupled device (CCD) cameras which comprise a large number of photosensitive detectors which are grouped, such as in a flat rectilinear array. Each detector includes a photosensitive front and a pair of electrical outputs through which electrons are emitted when light of a predetermined range of wavelengths shines on the photosensitive front. The outputs of the detectors of the CCD camera are input to a processing unit for analysis as needed. CCD cameras are used for various purposes in which the position, intensity, and wavelength of light needs to be recorded as an electrical signal to be analyzed electronically.